Ecological networks of dissolved organic matter and microorganisms under global change

Microbes regulate the composition and turnover of organic matter. Here we developed a framework called Energy-Diversity-Trait integrative Analysis to quantify how dissolved organic matter and microbes interact along global change drivers of temperature and nutrient enrichment. Negative and positive interactions suggest decomposition and production processes of organic matter, respectively. We applied this framework to manipulative field experiments on mountainsides in subarctic and subtropical climates. In both climates, negative interactions of bipartite networks were more specialized than positive interactions, showing fewer interactions between chemical molecules and bacterial taxa. Nutrient enrichment promoted specialization of positive interactions, but decreased specialization of negative interactions, indicating that organic matter was more vulnerable to decomposition by a greater range of bacteria, particularly at warmer temperatures in the subtropical climate. These two global change drivers influenced specialization of negative interactions most strongly via molecular traits, while molecular traits and bacterial diversity similarly affected specialization of positive interactions.


Statistics
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Software and code
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Data
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Ecological, evolutionary & environmental sciences study design
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Study description
Macroecological experiments performed in China and Norway by considering two environmental gradients for aquatic microcosms: Temperature and nutrient. We examined sediment DOM compositions and their association with bacteria.

Research sample
There are 300 microcosms for bacterial communities, including 5 elevations from two mountains. For each elevation, ten nutrient levels with three replicates. Such a large number of 300 samples such as 5 elevations and 10 nutrient levels across two mountains enable us to statistically explore the relationships among microbes, DOM and environments.

Sampling strategy
We

Data exclusions
We have three replicates for each treatment. There were no data exclusions as we successfully obtained all necessary results for each sample.

Reproducibility
We performed the experiments in the described months in each mountain for one month and applied three replicates for each treatment. All replicates were successful. All details in field setups, laboratory analyses, and data analyses described for reproducibility in the material and methods.

Randomization
Samples were reordered for sampling handling, FT-ICR MS, DNA extraction, PCR amplification and sequencing to rule out potential biases. The randomization is generally not relevant to our study results as our experiments have quality controls in the tests such as with standards in FT-ICR MS.